1. Field of the Invention
The present invention relates to an image holding (or carrying member for holding (or carrying) electrostatic latent images and/or toner images. The image holding member according to the invention is intended to be used principally in electrophotography.
2. Description of the Prior Art
Hitherto as an image holding member for use in electrophotography there have been known and used two types of image holding members, one of which is an electrophotographic photosensitive member and the other consists of a group of image holding members other than the electrophotographic photosensitive member. The first mentioned electrophotographic photosensitive member has a great variety of arrangement and may be designed so as to meet the characteristics requirements as then desired and to well suit to the electrophotographic process as then employed.
A typical example of electrophotographic photosensitive member in use widely is designed to provide its surface with an insulating surface layer. This insulating surface layer is provided for the purpose of protecting the photoconductive layer as well as improving the mechanical strength and the dark decaying property of the member. Also, the provision of an insulating surface layer is necessary to make the member adoptable in a certain particular electrophotographic process. Various representative examples of the photosensitive member provided with such an insulating surface layer and the electrophotographic process in which such a photosensitive member is used, are disclosed, for example, in U.S. Pat. No. 2,860,048 and Japanese Patent Publication Nos. 16429/1966, 15446/1963, 3713/1971, 23910/1967, 19747/1967 and 4121/1961.
When the electrophotographic photosensitive member is subjected to a specific electrophotographic process, an electrostatic latent image is formed thereon which is visualized by developing with a toner.
As to another image holding members, some representative examples thereof will be described hereinafter.
An electrostatic latent image formed on the electrophotographic photosensitive member having a photoconductive layer by a certain electrophotographic process is usually developed with a toner and then the toner image thus formed is transferred to a suitable recording member such as a sheet of paper. According to other electrophotographic process as disclosed, for example, in Japanese Patent Publication Nos. 7115/1957, 8204/1957 and 1559/1968, the electrostatic latent image formed on an electrophotographic photosensitive member is at first transferred to an electrostatic latent image holding member on which the transferred latent image is developed with a toner and thereafter the toner image is transferred to a recording member. This modified process contributes to the improvement of repeating usability of the electrophotographic photosensitive member.
Further modifications of the electrophotographic process are disclosed, for example, in Japanese Patent Publication Nos. 30320/1970 and 5063/1973 and Japanese Patent Application laid open No. 341/1976. These modifications are used to form on an electrostatic latent image holding member an electrostatic image corresponding to the electrostatic image formed on an electrophotographic photosensitive member. In the modifications, there is used an electrophotographic photosensitive member in the form of a screen having a plurality number of fine openings on which an electrostatic latent image is formed by a specific electrophotographic process. Through the electrostatic latent image formed on the electrophotographic photosensitive member, a corona charging treatment is conducted for the electrostatic latent image holding member so as to form thereon an electrostatic latent image by modulating the ion stream of corona. The electrostatic latent image formed on the image holding member is then developed with a toner and the developed image is transferred to a recording member to obtain the final image.
Furthermore there is known such a process according to which the toner image formed on the electrophotographic photosensitive member or the electrostatic latent image holding member is not directly transferred to the recording member, but it is transferred at first to a toner image holding member and then to a recording member on which the toner image transferred from the toner image holding member is fixed. This process is particularly effective for forming a color image or for carrying out a high speed copying. As the recording member, high flexible material such as sheet of paper and film is generally used. Therefore, it is somewhat difficult to transfer a tricolor image to such a recording material while maintaining accurate alignment (or registration) of the color components of the image. The process in which a toner image holding member that may be made of a hardly deformable material is used, has an advantage in view of accurate alignment of the color image components. Namely, a well aligned color image can be formed by at first transferring the color components of a tricolor image to a hardly deformable toner image holding member and thereafter transferring the toner image on the member to such a recording member all at once. Also, by using the process in which a toner image is transferred to a recording member through a toner image holding member, a substantial speed up of copying operation may be attained.
As will be seen from the foregoing, it is very important for an image holding member, which may be an electrophotographic photosensitive member or other member having no photoconductive layer used for holding an electrostatic latent image or toner image, to have a particular electric characteristic suitable to the electrophotographic process then used. Besides, durability and cleaning property are other important properties which such an image holding member should have. A high durability is required when the image holding member must be repeatedly used. The cleaning property is indispensable for determining the easiness of the removal of any residual toner adhered to the surface of the image holding member. To obtain a clear and sharp image and also to prevent the associated cleaning means from being damaged, the cleaning property is of critical importance. For the reason, various attempts have been made to improve the durability and cleaning property of the image holding member. The provision of a surface layer having excellent durability is one typical solution of the problem. Examples of such a surface layer applied onto a photoconductive layer, insulating layer or electric conductive layer include thin layers of vinyl cellulose, ethyl cellulose, acrylic urethane, polyparaxylylene, aluminum oxide and titanium oxide. Also, it is known to overlay a film sheet of polyethylene terephthalate, polyethylene, polypropylene and polystyrene on the photoconductive layer by using a suitable bonding agent or to vapour-deposit an inorganic material such as mica onto the layer. Among them, teflon, polyethylene, polyethylene terephthalate and vinylidene fluoride resins and the like are preferable ones useful for forming a surface layer having excellent lubrication property, durability and cleaning property.
However all these materials are in the form of film sheet and therefore they necessitate a high standard bonding technique by which the material in the form of film sheet can be adhered to a photoconductive layer, insulating layer or electric conductive layer with a suitable bonding agent. This brings forth only a relatively low efficiency. Furthermore, it is almost impossible to form a seamless surface layer on an image holding member in the shape of drum. With acrylic urethane or epoxy resin it may be possible to form a surface layer by coating techniques. But, the surface layer thus formed lacks adequate lubrication property, durability and cleaning property.
Another disadvantage of an image holding member provided with a conventional surface layer is an insufficient moisture resisting property. When the image holding member is used for a long time in the atmosphere of high humidity, the characteristics of the member is adversely affected and therefore the quality of image formed thereon is remarkedly deteriorated.